Document Apache HTTP V5 Client

[acm19]

Documents Apache HTTP V5 Client. Fixes example for pre-5 versions of the client.

Pull Request Checklist:

• [ ] I have added a contribution line at the top of CHANGELOG.md.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[dblock]

Nice. Make a release!